The present invention relates to baker's yeast and, more particularly, to the provision of a free-flowing particulate baker's yeast having a moisture content in the range of from about 65 to 75 percent by weight.
Yeast which is used for baking purposes generally is produced and sold in two distinct forms, i.e., as fresh yeast having a moisture content of from about 65 to 75 percent by weight (which typically is the range of moisture which is obtained from standard mechanical dehydration (centrifugation/filtering) of cream yeast resulting from the propagation of yeast in commercial-scale fermentors), and as active dried yeast, having a moisture content generally below about 10 percent by weight (achieved by evaporative drying under controlled conditions).
Fresh baker's yeast is a popular form in which yeast is used in both commercial and home baking, and is provided for this purpose either in compressed form or in a "bulk" form in which the yeast is granular. Bulk yeast finds significant application in commercial baking operations in which continuous or semi-continuous metering of ingredients is required.
Owing to the high moisture content of bulk yeast, its maintenance in the required particulate, free-flowing form often presents difficulties. The bulk yeast comprises a mass of living yeast cells having varying amounts of extracellular water in the interstitial spaces between and surrounding the cells. Water also is a major component of the yeast cells per se (commonly referred to as internal or intracellular water), and the relative amounts of water inside of and external to the cells are largely governed by equilibrium considerations. In general, the greater the proportion of extracellular water, the wetter the consistency of the bulk yeast and the greater the tendency of the yeast to coalesce and become less free-flowing. The problems in establishing and maintaining free-flowability of bulk yeast become particularly aggravated with increasing storage time and with storage conditions in which temperature extremes are encountered.
Workers in the art have suggested a number of techniques for improving the flow characteristics of bulk yeast. One suggestion has been to dry the yeast to a lower moisture content, e.g., below about 65 percent by weight. While perhaps effective in establishing and maintaining good flow characteristics, this method adds considerably to the cost of granular yeast since it requires additional energy and labor. Moreover, for yeast manufacturing facilities in which a variety of yeast products are produced (e.g., both compressed yeast and bulk yeast), it often is impractical and disadvantageous to attempt to establish different dewatering and/or drying facilities and conditions for these products.
Other approaches to this problem involve the addition of various materials to the bulk yeast. For example, British Patent Specification No. 1,397,410 discloses a mixture of granulated yeast (either "moist" yeast having a dry matter content of from 27 to 45 percent by weight or "dried" yeast having a dry matter content of greater than 92 percent by weight) and from about 0.5 to 3.0 percent by weight (dry basis) of hydrophobic silicic acid in order to aid flowability. U.S. Pat. No. 4,232,045 discloses the incorporation of small amounts of non-deliquescent drying agents such as hydrophilic silicon dioxide, micronized wood pulp or micronized cellulose to bind or absorb extracellular moisture in a bulk yeast so as to maintain flowability over extended time periods. British Patent Specification No. 1,560,478 discloses the addition of from 0.5 to 25 percent by weight of a "solid, highly water-absorbing agent" to a granulated compressed yeast for the same purpose.
German Offenlegungsschrift No. 2651349 discloses the use of a combination of both a hydrophilic agent and a hydrophobic agent to improve the "shelf-life" and "pourability" of fresh baker's yeast. Particular examples in this publication describe the use of combinations of hydrophilic silica and hydrophobic silica and a combination of hydrophobic silica and a swelling starch. The published application also suggests the use of salts of higher fatty acids, such as magnesium stearate, as hydrophobic substances which can be employed along with a hydrophilic substance. However, it is disclosed that when such salts are employed, an organic acid also must be used in order to neutralize the "alkalizing action" of these salts.
Attainment of free-flowing bulk yeast through use of additives is a desirable goal and inherently less capital- and labor-intensive than resort to techniques which involve additional drying of the bulk yeast. However, utilization of additives necessarily requires concern for the compatability of the additives with yeast and the products in which the yeast is employed, as well as the effect of the additives on the ultimate functional properties of the yeast in baking. From simply a generalized economic and functional viewpoint, it is highly desirable that the additive be effective for its intended purposes at low levels and that use of the additive require neither special processing considerations nor use of a necessary co-additive (e.g., the previously disclosed need for use of an organic acid in systems where a combination of hydrophilic agent and a hydrophobic metal salt of a higher fatty acid is used). Similarly, from an aesthetic point of view, any additive(s) employed must not impart undesired colors, flavors, textures or aromas to the yeast or the products in which the yeast is to be used.
Study of the use of additives to establish and maintain free-flowing characteristics in bulk yeast indicates that broad generalizations with respect to anticipated functionality are of little value. For example, although the art broadly discloses the use of strongly water-absorbing agents to promote free-flow characteristics of bulk yeast, numerous additives falling within this class either fail in this purpose or produce bulk yeast products which, while free-flowing, exhibit reduced leavening activity as compared to an untreated bulk yeast. The same is true for a number of hydrophobic agents, whether used alone or in combination with other additives.